I can't speak for your schools, but it was in my history classes as well as commonly mentioned in almost every book about World War II in the Pacific I've read.
I think it’s safe to say that most Americans have little to no understanding of this history. Maybe “written out” is an exaggeration, but “quickly glossed over and afterward ignored” would be a fair summary.
That's different than 'written out of'.
Americans know little about the Astor expeditions to the Pacific Northwest, the Fremont expeditions, Californian independence and statehood, or any number of other things.
Do you think high school history textbooks should have detailed coverage of the Astor expedition, etc.? Or if not, what’s your point?